Tire tread

ABSTRACT

A tire tread for a pneumatic tire has a center rib and a series of steeply slanted grooves in each side region of the tread, the circumferentially adjacent grooves form blocks extending through the tread side regions. The center rib has a serrated configuration along each lateral side and a supporting chamfer extending from each serration point. Adjacent to each rib chamfer is a chamfer extending from the axially innermost point of the rib at the junction of two adjacent steeply slanted grooves. The rib is provided with high density siping. The tread blocks are siped wherein the siping density decreases from the tread center to the tread shoulders.

FIELD OF THE INVENTION

[0001] The present invention is directed to a tire tread with improvedperformance in snow and ice and in regular running conditions. The treadis provided with a central rib and a series of steeply slanted groovesadjacent the rib. The rib and the adjacent tread blocks are configuredto provide for improved all weather performance.

BACKGROUND OF THE INVENTION

[0002] In a conventional tire for typical use as on a passenger car orlight truck, the tire tread is provided with a series of grooves, eithercircumferentially or laterally extending, or a combination of both, toform a plurality of blocks.

[0003] The goals of a tire during winter driving condition are tomaintain good contact with the road, while providing for enhancedtraction. However, since enhanced traction is best achieved by providingmost biting edges to the tread pattern, while road contact is achievedby providing more surface area for tread contact, these goal are oftenconflicting.

SUMMARY OF THE INVENTION

[0004] The present invention is directed to a tire with improved winterdriving condition.

[0005] Disclosed is a pneumatic tire comprising a tread and shouldersadjacent the tread, the tread comprising a central region and a pair ofopposing side regions. The tread has a circumferentially extending ribin the central region, and a plurality of steeply slanted groovesinclined at an angle relative to the circumferential direction of thetire in each side region. The center rib has a plurality of sipesextending across the full width of the rib, the sipes having a densityof 2 to 8 sipes per inch (0.78-3.15 sipes per cm). Additionally, thesteeply slanted grooves in each side region initiate at the junction ofthe central region and the side regions and terminate in the shoulders,forming circumferentially adjacent tread blocks. The blocks extend fromthe central region to the shoulders and have a plurality of sipes. Thespacing between adjacent sipes in the block increases toward the treadshoulders. The tread has a greater sipe density in the central region ofthe tire than in the side regions.

[0006] In one aspect of the invention, at the axially inner portion ofthe block, the block has a sipe density of 1 to 5 sipes per inch(0.393-1.97 sipes/cm). At the axially outer portion of the block, theblock has a sipe density of 0.5 to 3 sipes per inch (0.2 to 1.18sipes/cm).

[0007] In one aspect of the tire, the lateral edges of the rib have aplurality of laterally extending edges and circumferentially extendingedges. The laterally extending edges on each side of the rib arecircumferentially offset from the laterally extending edges on theopposing side of the ribs. Preferably, extending from the laterallyoriented edges of the rib, and along the lateral edge of the rib, arechamfers that decrease in width from the laterally oriented edge to thecircumferentially adjacent laterally oriented edge.

[0008] In another aspect of the invention, the radial height of the ribchamfer gradually decreases from the laterally oriented edge to thecircumferentially adjacent laterally oriented edge.

[0009] In another disclosed aspect of the invention, to increase the ribflexibility as the tread wears, the sipes of the tread rib extend intothe chamfers.

[0010] The sipes in the tread rib are formed of at least two inclinedportions. When formed of two portions, the sipe portions ideally followthe same inclination angle as the laterally oriented edges of the rib.In one embodiment, the sipes are formed of three portions.

[0011] The sipes in the tread blocks are preferably orientedperpendicular to the steeply slanted grooves. The tread block sipes mayalso be inclined in the same direction as the most adjacent sipe portionof the tread rib.

[0012] In another aspect of the tire, the steeply slanted grooves have anon-constant width as the grooves extend from the central region to theshoulders, the grooves having a maximum width in the central 15% of eachside region of the tread. The grooves may have a maximum width of atleast 1.5 times the minimum groove width of the steeply slanted grooves.

[0013] In another aspect of the invention, the net-to-gross ratio of thetire decreases from the tread edge toward the tread center, with amaximum net-to-gross ratio at the equatorial plane of the tire.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be described by way of example and withreference to the accompanying drawings in which:

[0015]FIG. 1 is a plan view of the tire;

[0016]FIGS. 2-5 are various embodiments of the rib chamfers;

[0017]FIGS. 5a-5 b are cross sectional views taken of the chamfer ofFIG. 5;

[0018]FIG. 6 is a portion of the rib and a chamfer illustrating anotherembodiment of the siping; and

[0019]FIG. 7 is another alternative of the tread.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The following language is of the best presently contemplated modeor modes of carrying out the invention. This description is made for thepurpose of illustrating the general principals of the invention andshould not be taken in a limiting sense. The scope of the invention isbest determined by reference to the appended claims.

[0021]FIG. 1 is a plan view of a tread for a tire in accordance with thepresent invention. The tread configuration is intended for use on apassenger vehicle, or a light truck. The illustrated tread has adirectional configuration, with the preferred direction for forwardmoving being that shown by the arrow D. The tread is divided into threeregions, a central region A, and two side regions B. The central regionis centered on the equatorial plane of the tire and has a width ofapproximately 15% to 30% of the tread width W, the tread width beingmeasured from one tread shoulder to the opposing tread shoulder.

[0022] When operating in winter driving conditions, the central regionof the tire has the most impact on the performance of the tire. In thepresent tire tread, the center of the tread is provided with acontinuously extending rib 10. The rib 10 has sipes 12 extending acrossthe full lateral width of the rib 10. The rib 10 has a heavy sipedensity, within the range of 2 to 8 sipes per inch (0.78 to 3.15sipes/cm), with a preferred density of 3 to 7 sipes per inch (1.18 to2.76 sipes/cm). The presence of the rib 10 provides good ground contactof the tire, while the heavy siping of the rib 10, and thus the centralregion of the tire tread, provides for increased traction as themultiple sipes 12 flex open providing tread edges when the treadcontacts the ground.

[0023] The rib sipes 12 have a non-linear configuration of at least twoinclined portions. The sipes 12 in FIG. 1 are formed of two inclinedportions 14, 16. The inclined portions 14, 16 are placed atsubstantially similar, but oppositely inclined angles to form an inverseV configuration, wherein the apex of the V is located at approximatelythe equatorial plane EP of the tire. The spacing betweencircumferentially adjacent sipes 12 is constant, but may be varied topermit pitching of the tire for optimization of the noisecharacteristics of the tire.

[0024] The sides 18, 20 of the rib 10, when viewed from above, has anextended, serrated configuration at the surface of the rib 10 thatcontacts the ground when the tread is new and not-worn. Each serration22 is formed from a laterally oriented edge 24 and an inclinedcircumferentially extending edge 26; the junction of the two edgesforming a serration point. The serrations 22 on each side 18, 20 of therib 10 are laterally offset from each other. The laterally oriented edge24 has a high inclination angle relative to the equatorial plane EP,while the circumferentially extending edge 26 has a low inclinationangle relative to the equatorial plane EP.

[0025] Extending from the laterally oriented edge 24 along each side 18,20 of the rib 10 is a chamfer 28. The chamfer 28 extends in acircumferential direction from the laterally oriented edge 24 of theserration 22 to the next circumferentially adjacent serration 22, alongthe side 18, 20 of the rib 10.

[0026] Due to the chamfer 28, at the tread depth the rib 10 has analmost straight configuration. The chamfers 28 have a greatest widthwhere the chamfer 28 initiates at the laterally oriented edge 24 of theserration 22. The width of the chamfer 28 narrows as the axiallyoutermost edge 30 of the chamfer 28 is substantially parallel to theequatorial plane EP of the tire while the sides 18, 20 of the rib 10 areinclined in the circumferential direction. The provision of the chamfers28 behind the heavily siped rib 10 provides support for the rib 10 asthe sipes 12 flex open, strengthening the rib 10 and maintaining goodground contact pressure for the rib 10.

[0027]FIG. 2 illustrates a side view of the chamfer 28. The chamfer 28has a maximum width at the laterally oriented edge 24 of the serration22, and gradually decreases in width as the chamfer 28 approaches thenext adjacent serration point 22. Concurrently, the height h of thechamfer 28, as measured from the base of the tread depth, graduallydecreases in the circumferential direction.

[0028]FIG. 3 illustrates a variation of the chamfer 28. The uppersurface of the chamfer 28 is multi-planar. Where the chamfer 28 connectswith the laterally oriented edge 24, the surface is defined by a radiusof curvature R1 located inward of the upper surface of the chamfer 28.Towards the base of the chamfer 28, the top surface is defined by aradius of curvature R2 located outward of the upper surface of thechamfer 28.

[0029] The chamfer 28 of FIG. 4 is a variation of that of FIG. 3 whereina flat ledge 34 is employed along the mid-length of the chamfer 28. Thechamfer 28 forms a tangency to a circle at several locations, as seen byR3 and R4.

[0030] In another embodiment of the chamfer 28, FIG. 5, the top surfaceof the chamfer 28 has a different multi-planar configuration. At themaximum lateral width, the top surface of the chamfer 28 slopes downwardtoward the tread edge, see FIG. 5a. As the chamfer width decreases, theaxially outer edge 30 of the chamfer 28, relative to the equatorialplane EP of the tire, gradually increases in height relative to the fulltread depth. Concurrently, the axially inner edge 36 of the chamfer 28decreases in height, see FIG. 5b. Thus, as the width of the chamfer 28decreases, the height increases, causing the outer surface of thechamfer 28 to twist.

[0031] If maintaining tread flexibility as the tread is worn is desired,the sipes 12 in the center rib 10 may extend into the chamfers 28, seeFIG. 6. When the tread is unworn, the sipes 12 in the chamfers 28 do notopen during rotation as there is no contact with the road surface, andthe chamfer 28 continues to provide support to the rib 10. After thetread begins to wear, and the uppermost surface of the chamfer 28 slowlybecomes part of the ground contacting surface of the tread, theeffective rib width increases, and the siping of the chamfer 28 beginsto interact with the remaining tread. In effect, sipes 12 in the chamfer28 act as increased grooving of the tread as the tread depth decreasesdue to wear.

[0032] The laterally oriented edge 24 of each serration 22 is inclinedat an angle of equal or less than 90°, but no less than 45° relative tothe equatorial plane EP. In the tread of FIG. 1, the laterally orientededge 24 of each serration is inclined at approximately 45° relative tothe equatorial plane EP. The laterally oriented edges 24 of eachserration 22 on each side 18, 20 of the rib 10 are inclined as offsetmirror images of the each other. The circumferentially extending edge 26is inclined at angle of approximately 0° to 30° relative to theequatorial plane EP of the tire. When the circumferentially extendingedges 26 are substantially parallel to the EP, then thecircumferentially adjacent laterally oriented edges 24 are inclined inopposing directions; or else the rib 10 will “walk” across the tread.Because the chamfers 28 extend from the laterally oriented edges 24, thechamfers 28 on each side 18, 20 of the rib 10 extend in the samedirection.

[0033] Adjacent to the center rib 10, in each side region B of thetread, are a plurality of steeply slanted grooves 38. The grooves 38 ineach side region B of the tread are circumferentially offset from thegrooves 38 in the opposing side region B. The grooves 38 initiate at thejunction of the center region A and the side regions B. At the junction,the grooves 38 have a very low angle of inclination relative to the EPof the tire tread, and gradually increase in inclination. The majorityof each groove 38 has a inclination angle α of 20° to 50° relative tothe circumferential direction of the tire, as measured by the centerlineof the groove 38.

[0034] As the grooves 38 traverse the side regions B of the tread, thegroove width varies. Close to the central rib 10, the groove width isrelatively large, though partially consumed by the chafer 28, and as ittraverses the side region, the width decreases and then widens outbefore decreasing again at the tread edge. The region of relativelygreater width in the central portion of the groove 38 is located atapproximately the mid-point of the side regions B. The portion of thegroove 38 with the greatest width, as measured perpendicular to thegroove centerline, has a maximum width Wx of 1.5 times the width Wn ofthe minimum groove width of the steeply slanted grooves 38.

[0035] As the tread edge, the inclination angle of the groove 38increases, approaching 85°. At the tread edge, the grooves have an angleof 70°-85°.

[0036] Circumferentially adjacent steeply slanted grooves 38 formcircumferentially adjacent rib blocks 40. The blocks 40 initiateadjacent to the rib 10 and extend to the tread edge. At the tread edge,the block width increases. The blocks 40 extend continuously through theside regions B, however, if desired for increased water flow andtraction, circumferential grooves may be provided in the side regions Bto form smaller blocks.

[0037] At the axially innermost edge 42 of the blocks 40, and extendinginto the junction of adjacent steeply slanted grooves 38, are extendingsloping chamfers 44. Each chamfer 44 has a circumferential length of{fraction (1/60)}^(th) to {fraction (1/40)}^(th) of the circumferentiallength of the tire. Relative to the circumferential length of theassociated tread block 40, the chamfer 44 has a length of 5% to 20% ofthe block length, the block length being measured along parallel to theequatorial plane and exclude the chamfer length.

[0038] As the chamfer 44 extends into the junction of the grooves 38,the area of the grooves decreases with increased height of the chamfer44. However, due to the positioning of the block chamfer 44 adjacent tothe rib chamfers 38, the ability for water to flow into the grooves 38is not compromised. As the rib chamfer 28 decreases in width and height,the block chamfer 44 increases in width and height. The placement of thecircumferentially extending rib chamfers 28 in combination with thepredominately circumferentially extending block chamfers 44 effectivelyapproximate a pair of wide circumferential grooves. Thus, water flow inthe tread is maintained, as is the stiffness of the central treadregion.

[0039] The rib chamfer 44 can have any of the chamfer profiles as shownin FIGS. 2-5. When the chamfer of FIG. 5 is used as the rib chamfer 44,the chamfer edge that decreases in height should be the axially outeredge, relative to the EP. By placing this edge as the outer edge, wateris diverted into the grooves adjacent the rib 10.

[0040] The net-to-gross ratio of the tread, and the various regions ofthe tread, reflects the ability of the to move water. When viewed withjust two zones, as illustrated in FIG. 1, the center region has anet-to-gross ratio of 50 to 63% and each side region has a net-to-grossratio of 55 to 70%.

[0041] To more fully appreciate the water flow capability of the tread,additional zones may be identified in each tread half. The zone Fencompassing the effectively created wide circumferential groovescreated by the adjacent chamfers, as measured from the axially innermostedge of the rib chamfer 28 and the axially outermost edge of the blockchamfer 44 has a net-to-gross ratio of 22 to 35% when the tread is new.As the tread wears, this net-to-gross ratio increases. From the axiallyoutermost edge of the block chamfer 44 to a location wherein the grooves38 begin to decrease in width, the zone C, has a net-to-gross ratio of50% to 65%. The axially outer edge of the tread, zone E, has anet-to-gross ratio of 75% to 85%, typically for the tread edges of atire to maintain tread edge stiffness. Extending from the tread edgetoward the tread center, the net-to-gross ratio decreases until itreaches a maximum at the tread center due to the rib 10.

[0042] Sipes 46 are spaced along the circumferential length of the block40. The sipe density is the greatest toward the tread center anddecreases in the direction of the tread edges. At the axially innerportion of the block 40, the sipe density has a maximum density of equalto the rib sipe density with a minimum density of 1 to 5 sipes per inch(0.393-1.97 sipes/cm). At the axially outer portion of the block 40, thesipe density is in the range of 0.5 to 3 sipes per inch (0.2 to 1.18sipes/cm). The variation in the block sipe density cooperates with thehigh density siping in the tread rib 10 to gradually vary the treadstiffness. Additionally, as noted previously, the heavier siping in thecenter of the tread improves the snow driving performance of the tire byincreasing the number of tread edges in the center of the tire whileproviding for a stiff tread at the outer tread zones.

[0043] At the axially outermost 25% of the each side region B, the sipes46 extend into the tread shoulders. To assist in water drainage andflexibility at the tread edge, the sipes 46 may have increased width, asillustrated at FIG. 1. Each sipe 46 in the shoulder has a wide widthportion 48 and a narrow width portion 50. In each block, the sipes 46are arranged so that the wide width portions 48 and the narrow widthportions 50 are circumferentially alternating.

[0044] For the directional tread illustrated in FIG. 1, the steeplyslanted grooves 38 in each side region B are mirror images, thoughlaterally offset, of the steeply slanted grooves 38 in the opposing sideregion B. Also, due to the directional nature of the tread, all of therib chamfers 28 are pointed in one direction and all the block chamfers44 are pointed in the opposing direction.

[0045]FIG. 7 illustrates the previously described tire tread as anon-directional tire tread. The steeply slanted grooves 38 in each sideregion B are laterally offset mirror inverse images of the grooves 38 inthe opposing side region B. The laterally oriented edges 24 of at thecenter one rib 10 are inclined in the same direction. To maintain theserrated configuration, the circumferentially extending edges 26 areinclined in the same direction, parallel to each other. The rib chamfers28 on opposing sides of the rib 10 point in opposing directions, whilethe block chamfers 44 in each side region B point in the oppositedirection from the block chamfers 44 in the opposing side region B.

[0046] The sipes 52 in the rib 10 of the non-direction tread are formedof three portions, wherein the first and third portions of the sipe 52are inclined at substantially equal inclination angles. The block sipesin the side regions B are inclined at angles substantially equal, but nomore than 10° greater, than the rib sipe portion located adjacent to therelative side region. In the instant tread, the overall sipe pattern forthe entire tread is inclined at an angle opposite that of the steeplyslanted grooves.

[0047] Other features of the non-direction tread may be identical tothat of the directional tread, with permissible variations in accordancewith those already discussed.

What is claimed is:
 1. A pneumatic tire comprising a tread and shouldersadjacent the tread, the tread comprising a central region and a pair ofopposing side regions, the tread further comprising a circumferentiallyextending rib in the central region, and a plurality of steeply slantedgrooves inclined at an angle relative to the circumferential directionof the tire in each side region, the rib having a plurality of sipesextending across the full width of the rib, the sipes having a densityof 2 to 8 sipes per inch (0.78-3.15 sipes per cm), and the steeplyslanted grooves in each side region initiate at the junction of thecentral region and the side regions and terminate in the shoulders,forming circumferentially adjacent tread blocks, the blocks extendingfrom the central region to the shoulders, and having a plurality ofsipes, the spacing between adjacent sipes increasing toward the treadshoulders, wherein the tread has a greater sipe density in the centralregion of the tire than in the side regions.
 2. The tire of claim 1wherein the lateral edges of the rib have a plurality of laterallyextending edges and circumferentially extending edges, the laterallyextending edges on each side of the rib being circumferentially offsetfrom the laterally extending edges on the opposing side of the ribs. 3.The tire of claim 2 wherein extending from the laterally oriented edgesof the rib, and along the lateral edge of the rib, is a chamfer thatdecreases in width from the laterally oriented edge to thecircumferentially adjacent laterally oriented edge.
 4. The tire of claim3 wherein the radial height of the rib chamfer gradually decreases fromthe laterally oriented edge to the circumferentially adjacent laterallyoriented edge.
 5. The tire of claim 3 wherein the sipes in the tread ribextend into the chamfer.
 6. The tire of claim 1 wherein the sipes in thetread rib are comprised of at least two inclined portions.
 7. The tireof claim 1 wherein the sipes in the blocks are oriented perpendicular tothe steeply slanted grooves.
 8. The tire of claim 1 wherein the sipes inthe tread rib have two sections formed of portions inclined at equal butopposing angles and the sipes in the blocks are inclined in the samedirection as the most adjacent sipe portion in the tread rib.
 9. Thetire of claim 1 wherein the steeply slanted grooves have a non-constantwidth as the grooves extend from the central region to the shoulders,the grooves having a maximum width in the central 15% of each sideregion of the tread.
 10. The tire of claim 9 wherein the grooves have amaximum width of at least 1.5 times the minimum groove width of thesteeply slanted grooves.
 11. The tire of claim 1 wherein the sipes inthe axially outermost 25% of each side region extend into the treadshoulders.
 12. The tire of claim 11 wherein each sipe extending into theshoulder has a wide and a narrow width portion such that the wide widthportion of each sipe in a single block is circumferentially adjacent toa narrow width portion of the adjacent block.
 13. The tire of claim 1wherein at the axially inner portion of the block, the block has a sipedensity of 1 to 5 sipes per inch (0.393-1.97 sipes/cm) and at theaxially outer portion of the block, the block has a sipe density of 0.5to 3 sipes per inch (0.2 to 1.18 sipes/cm).
 14. The tire of claim 1wherein the net-to-gross ratio of the tire decreases from the tread edgetoward the tread center, with a maximum net-to-gross ratio at theequatorial plane of the tire.